Turbine engines are used as the primary power source for many types of aircrafts. The engines are also auxiliary power sources that drive air compressors, hydraulic pumps, and industrial gas turbine (IGT) power generation. Further, the power from turbine engines is used for stationary power supplies such as backup electrical generators for hospitals and the like.
Most turbine engines generally follow the same basic power generation procedure. Compressed air generated by axial and/or radial compressors is mixed with fuel and burned, and the expanding hot combustion gases are directed against stationary turbine vanes in the engine. The vanes turn the high velocity gas flow partially sideways to impinge on the turbine blades mounted on a rotatable turbine disk. The force of the impinging gas causes the turbine disk to spin at high speed. Jet propulsion engines use the power created by the rotating turbine disk to draw more air into the engine and the high velocity combustion gas is passed out of the gas turbine aft end to create forward thrust. Other engines use this power to turn one or more propellers, fans, electrical generators, or other devices.
Low and high pressure compressor (LPC/HPC) components such as compressor blades and impellers are primary components in the cold section for any turbine engine, and are typically well maintained. The LPC/HPC components may be subjected to stress loadings during turbine engine operation, and also may be impacted by foreign objects such as sand, dirt, and other such debris. The LPC/HPC components can degrade over time due to wear, erosion, foreign object damage, and other factors. Sometimes LPC/HPC components are degraded to a point at which they may need to be repaired or replaced, which can result in significant operating expense and time out of service.
There are several traditional methods for repairing damaged turbine engine components, and each method has some limitations in terms of success. One primary reason for the lack of success is that the materials used to make LPC/HPC components do not lend themselves to efficient repair techniques. For example, titanium alloys are commonly used to make impellers because the alloys are strong, light weight, and highly corrosion resistant. However, repairing an impeller with conventional welding techniques subjects the impeller to high temperatures both during the welding operation and during any pre- or post-welding heat treatment. This high temperature has resulted in warpage to impeller structures.
Nevertheless, there is a continuing need for improved repair methods that allow quicker repairs that minimize the need to scrap expensive parts. The modern jet aircraft is a very high capital thing. Gas turbine engines, for example, include many expensive components with complex shapes; impellers are one example of such a component. The complex design, and expensive materials, that are used to fabricate impellers often means that they can be quite expensive. As a consequence of these design and material criteria, it is desirable to repair damaged impellers when possible. The geometry of turbine engine impellers makes them particularly vulnerable to heat-related warping. The challenge is to heat the part to the temperatures needed for welding repair while retaining the part's geometry.
Accordingly there is a need for an apparatus and method to protect impellers from welding damage that arises from high temperatures. It is desired that the apparatus be able to prevent excessive warping of the impeller shape. Further, it is desired that the apparatus, and method of using the apparatus, be suitable for use with automated welding systems. It is thus desired that the efficiency of automated welding systems not be unduly compromised by the protective apparatus and method. The present invention addresses one or more of these needs.